Kieseloolite Formation v092014
Kieseloolite Formation (emended)
Authors: Dusar, M.; Deckers, J.; Matthijs, J.; Walstra, J.; Westerhoff, W.E.
Posted as discussion document for Paleogene-Neogene Subcommission at NCS website on 12.9.2014.
Name: The name is derived from silicified oolithic limestones outcropping around the Vosges massif in Alsace-Lorraine (France), rarely found as pebbles in the Meuse and Rhine gravels. The name has been introduced for the Lower Rhine graben by Kaiser (1907), and used in the Netherlands soon after (Tesch, 1908). The formation has been formally described by Westerhoff (2003). In Belgian lithostratigraphy, the ‘Kiezeloöliet Formation’ (Laga et al., 2001 after Sels et al., 2001) is in need of revision after the H3O project (Deckers et al., 2014).
Dutch spelling is Kiezeloöliet Formatie.
Stratotype:
In the German Lower Rhine Graben the Erft Block has been designed as the type area for the fluviatile facies of the Kieseloolith Schichten (Klostermann, 1992). In the Netherlands, borehole 60D1033 at Broeksittard, depth interval 19,00 – 201,00 m below the surface has been designed as the reference section in van Adrichem Bogaert & Kouwe (1993), referred to as lectostratotype by Westerhoff (2003).
Belgian parastratotype: Exploration borehole Maaseik – Jagersborg, drilled 1980, published in 2005 by Vandenberghe et al.; GeoDoc 049W0220; Lambert coordinates x 246636, y 200835, ground level (= zero level) +33,14 m TAW.
Depth interval: 62 – 166 m (depth according to Vandenberghe et al, 2005) or 63,20 – 164 m (depth according to log, in annex).
Subdivided in two members:
Brunssum Member: 62 – 127 m in borehole Maaseik – Jagersborg;
Waubach Member: 125,8 – 164 m (depth according to Vandenberghe et al., 2005) or 127-166 m (logging depth) in borehole Maaseik – Jagersborg.
Note that Vandenberghe et al. (2005) had a different concept of the Kieseloolite Formation, which incorporated the Jagersborg Member (22 – 72 m), thus ranging from 22 to 164 m. The Jagersborg Member is no longer retained in favour of the Stramproy Formation (corresponding to the major sandy part from 22 to 62 m in borehole Maaseik – Jagersborg), whereby the clay beds above the Brunssum I member (sensu common use in Belgium, Van der Sluys, 2000, accepted in Laga et al., 2001) have been included in the Kieseloolite Formation (62 – 72 m, hydrostratigraphic unit KI-k-1)
Description(from Deckers et al., 2014; Dusar et al., 2014):
The Kieseloolite Formation consists of fluvial sediments, deposited by precursors of Rhine and Meuse. These rivers drained the uplifted Ardenno-Rhenish massifs, eroded and transported the strongly weathered cover deposits of the Tertiary peneplain towards the NW. The sediments therefore predominantly consist of quartz sands with very stable heavy minerals association. Time of deposition coincided with active rift tectonics, characterised by thick sequences of rather coarse, gravel-bearing sand deposits, interrupted by periods of sediment starvation characterised by widespread deposits of clay with intercalated peat formation in the lower floodplain.
Two units can be distinguished, which are assigned member status, from bottom to top:
- Waubach Member
The Waubach sand member is quite regular in distribution and thickness, on average 60 m and generally coarse-grained (150 – 2000 µm). Lithified Waubach sand is outcropping in between the Geleen and Heerlerheide fault branches of the Feldbiss fault bundle, south of Neeroeteren: along the lower slope of the High Campine Plateau in Bergerven. Waubach sands are still poorly exposed in the adjoining former sand pit (now a leisure centre), where is has been extracted as ‘Neeroeteren Sand’ (Geys, 1972). It corresponds to the Hauptkies in the Lower Rhine Graben.
In geophysical well logs, this unit can be easily recognised by one or several coarsening upward sequences and the characteristic low values of the gamma-ray. On top this is completed by a sand unit in the 10 to 20 m thickness range without granulometric trends, displaying a facies already characteristic for the sand units incorporated in the succeeding Brunssum Member. It is remarkable that this top unit, occurring in the interval 127-148 m in borehole Maaseik - Jagersborg has been tentatively named ‘Lower Pey Sand’ in Vandenberghe et al. (2005). It is sedimentologically interpreted as a change from a braided river system to a meandering river system.
The clayey intervals are poorly developed, notwithstanding lowering of the resistivity curves. As a result the Waubach sand member is considered as a single permeable hydrogeological unit, at least in the rather small Belgian part of the Rur Valley Graben, of great importance as a productive and high capacity aquifer.
- Brunssum Member
Clay, brownish to black when charged with organic material, slightly sandy to silty, associated with lignite layers, with fine to moderately coarse sand intercalations of rapidly changing thickness, from decimetric to decametric scale (Brunssum Clay, Doppert et al., 1975). The clay is generally compact and stiff, with thicknesses of the metric scale, hence of aquiclude value. Occasionally, light coloured and kaolinitic clay layers are observed.
In geophysical well logs, the Brunssum Member is characterised by the occurrence of clay layers, which constitute the resistivity minima, interspersed with several permeable sand layers, with high resistivities. Two clay beds representing a resistivity minimum have been widely recognised in the area Bree – Maaseik, and were given member status, namely the Brunssum I and Brunssum II clay (in the Netherlands, in the area near Echt and Pey, a similar sequence of two clay layers are informally assigned as upper and lower Brunssum Clay, lithostratigraphically ranked as beds.
In drilling practice it is of utmost importance to recognise these clay layers, especially the lowermost Brunssum II clay bed, because these separate the confined from the vadose aquifers. Productive intercalated sand bodies between the Brunssum I and Brunssum II clay beds are named Pey Sand (Member) [formal spelling as Peij]. However, there is limited lateral consistency in these sand intercalations, which may rapidly change in facies and thickness, from 1 to 30 m. Similarly productive but younger sand layers between the Brunssum I clay and overlying clay bed have also been associated with Pey sand, in piezometers north of Maaseik.
Indeed, on top of the Brunssum I clay beds, more clayey layers may be distinguished, but rarely reach the resistivity minima characteristic for the Brunssum I and Brunssum II beds. The number of clay layers increases towards the SE in the Belgian part of the Rur Valley Graben. Especially South of Maaseik, splitting of clay layers and lignite seams makes it difficult to draw consistent boundaries between clay-sand units and use these as a basis for lithostratigraphic subdivision. Therefore the more detailed lithostratigraphical subdivision of the Brunssum Member has been abandoned.
Hydrogeological units, introduced by H3O project (Deckers et al., 2014):
Underlying strata:
Deposits of the Kieseloolite Formation are generally overlying those of the Breda Formation. The boundary is sharp, with a clear contrast between coarse, quartz-rich whitish sands of the Kieseloolite Formation and finer, glauconite-bearing grey-green sands of the Formation of Breda, and can be recognised instantly from the colour of the drilling mud. In the area around Maaseik, the Formation of Inden is intercalated between Breda and Kieseloolite formations. The Inden Formation displays facies characteristics similar to the overlying Waubach sands but which are dark coloured because of high organic content and a greater portion of fines. In any case, the contact with the marine Neogene, grouped in the Formation of Breda, remains the most important boundary for mapping and hydrological purposes.
Towards the western part of the Belgian Rur Valley Graben, another transitional deposit between Inden Formation and Kasterlee Formation occurs, provisionally assigned to the Breda Formation, but in drilling practice mostly associated with the overlying Kieseloolite Formation.
Overlying strata:
The Kieseloolite deposits are covered by the sandy deposits of the Stramproy Formation over the major Belgian part of the Rur Valley Graben. The sands of the Stramproy Formation are generally finer grained, the clay with lignite intercalations are less thick and compact than those of the Kieseloolite Formation and do not act as hydrogeological barriers.
In the extreme south, between the Geleen and Heerlerheide faults, the Kieseloolite Formation is outcropping on the margin of the Campine Plateau (Neeroeteren – Bergerven) or is unconformably covered by the Meuse river terraces grouped into the Beegden Formation.
Area: The entire Belgian part of the Rur Valley Graben, north-east of the Heerlerheide to Reppel Faults (Feldbiss fault system). To the west and southwest, on the upthrown side of the faults, contemporaneous deposits are assigned to the Formation of Mol (partim).
Thickness: The thickness of the Kieseloolite Formation in Maaseik – Jagersborg borehole slightly surpasses 100 m. Time of deposition coincided with high subsidence of the graben, creating accommodation space for sedimentation. On average the thickness varies between 100 m and 150 m but may reach 200 m in The Netherlands.
Age: Pliocene (with reference to Reuverian, Brunssumian, Susterian pollen-based continental substages of authors).
Discussion
The Kieseloolite Formation forms the core of a lithostratigraphic group provisionally named ‘the continental Neogene Group’. This group further includes the Inden, Stramproy and Mol Formations.
The lithostratigraphic subdivision of the Kieseloolite Formation was based on different principles. Originally, a palynological distinction was made between the clay beds outcropping at Reuver and Brunssum. This formed the basis for a twofold chronostratigraphic subdivision of the Pliocene into Reuverian and Brunssumian, applicable to the Kieseloolite Formation, which spans most of the Pliocene. However, this palynozonation is facies-dependent, even impractical for defining a biostratigraphic boundary. Its chronostratigraphic use is no longer supported (Kemna & Westerhoff, 2007; Donders et al., 2007). To add confusion, the same names are applied as lithostratigraphic beds which do not necessarily correlate with their chronostratigraphic homonyms.
Based on the same palynological interpretation, Vandenberghe et al. (2005) identified in borehole Maaseik – Jagersborg a Reuverian sequence and the Reuver Clay. However, there is no straightforward correlation possible between the Reuver Clay type area on the eastern Peel horst and the deposits assigned to the ‘Reuverian’ period in borehole Maaseik – Jagersborg; palynology was mainly used for defining the evolving facies characteristics, suggesting rather than confirming correlations.
The Brunssum Member, as currently defined, contained a series of units which had informal member status in Belgium and bed-status in South Limburg, and which are widely utilised for interpreting water wells (cf Van der Sluys, 2000). These were from bottom to top:
- Brunssum II clay (lower Brunssum bed in NL)
- Pey sand (also written Pey in Belgium)
- Brunssum I clay (upper Brunssum bed in NL)
The sequence is surmounted by Jagersborg / Schinveld (abandoned undefined denomination in NL) sand and clay beds, split between Stramproy and Kieseloolite Formations.
The clay beds in general and the Brunssum clays in particular are composed of several clay layers, with at least one plastic clay layer with minimal thickness of 1 meter able to act as a aquiclude, meaning a boundary layer in a hydrological system. Compact clay layers can be recognised by gamma-ray peaks and especially by the lowest resistivity values observed in the profile (Brunssum I, KI-k-2 or Brunssum II, KI-k-3 on borehole sections).
These units retain their value as hydrostratigraphic units but can no longer be used as lithostratigraphic units because of correlation obstacles due to frequent splitting and wedging out of sand and clay layers. It is rather the more complex sequences which were recognised and interpreted in lithostratigraphic terms, but their boundaries are not consistent over the graben area. Nevertheless in the region of Bree – Maaseik (north of the Elen-Neeroeteren fault) this subdivision is easily applicable. In the region of Elen – Rotem (between the Elen-Neeroeteren and Heerlerheide faults) at least the Brunssum I clay is confounded with the Schinveld beds. In the region of Neerpelt – Bocholt (in between the Grote Brogel and Bocholt faults) especially the clay beds wedge out.
The lithostratigraphical scale of Belgium established in 2001 (Laga et al., 2001) predates publication of the Memoir on borehole Maaseik – Jagersborg (Vandenberghe et al., 2005); instead it refers to the definition by Doppert et al. (1975) and the Dutch stratigraphical nomenclature (van Adrichem Bogaert & Kouwe, 1997), but deviates from the Dutch nomenclature by including the Jagersborg Member, named after borehole Maaseik – Jagersborg (Sels et al., 2001), which is now assigned to the Stramproy Formation. The lower part of the unit named ‘Waubach sand and gravel’ by Vandenberghe et al. (2005) at 166-193 m (surmounted by a clayey bed at 165 – 166 m)has been assigned to the Inden Formation. The whole unit is interpreted as a braidplain deposit; the fine fraction present in the Inden Formation but absent in the Waubach Member is at the basis for the distinction between both units.
In the region Hamont – Neerpelt – Bocholt (SW part of Rur Valley Graben) the Waubach Member becomes thicker. It is preceded by a sand unit of ca 50 m thickness, which is lateral equivalent to the Inden Formation, occurring more to the east, on the basis of geophysical well logs but which, lithologically, cannot be assigned to this formation. This sequence of quartz-rich sands, deposited in an estuarine setting contains sparse glauconite and occasionally abundant detrital lignite. This unit has been assigned to the Breda Formation (sensu Dutch stratigraphical nomenclator). However, drilling practice does not make a distinction with the overlying Waubach sands, whereas the transition to the underlying green sands (equivalent of Diest sands in the Breda Formation) is sharp and picked up as economic basement for water wells. This discrepancy between a practical lithological boundary (top of the green sands) and the lithostratigraphic boundary Breda – Kieseloolite Formation merits to be resolved.
The area south of the major graben boundary faults (from Peer to Opitter) contains fine sands which have been tentatively assigned in borehole descriptions either to the Kieseloolite – Waubach or Mol – Donk members. They have the characteristics of eolian sands blown out of the floodplain in the graben and deposited in the adjoining graben shoulder. No name has been introduced for this lithological unit.
The Mol Formation was described as a lateral equivalent of the Kieseloolite Formation. As the boundaries of the Kieseloolite Formation have been emended, the correlation with the Mol Formation needs more precision. The following correlation is proposed, from top to bottom:
Mol – Maatheide (MlMh) Stramproy Formation
Mol – De Maat (MlMa) Kieseloolite Formation Brunssum Member
Mol – Donk (MlDo) Kieseloolite Formation Waubach Member
The proposed correlation accounts for the Plio-Pleistocene transition derived from palynological change between ‘warm’ and ‘cold’ floras, observed both in the Mol and in the Stramproy / Kieseloolite Formations and for the thinning of the Brunssum Member and increasing hiatuses between Kieseloolite and Stramproy Formations towards the west in the Belgian part of the Rur Valley Graben. The boundary between the Donk and Maat Members seems to correspond with the base of the Brunssum II Clay Bed, supporting the correlation value of the latter unit.
The geographical boundary between Mol and Stramproy/ Kieseloolite Formations thus coincides with the main graben boundary fault, facilitating stratigraphic interpretation and mapping.
References
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The Belgian parastratotype for the Inden, Kieseloolite and Stramproy Formations, based on the stratigraphic study published in 2005 by Vandenberghe et al.: exploration borehole Maaseik – Jagersborg.
Subdivision of the Kieseloolite Formation and boundary with overlying and underlying formations in two reference sections between Bree and Maaseik. The proposed lithostratigraphical subdivisionintroduces two members, Waubach and Brunssum for the Kieseloolite Formation. The hydrostratigraphic units correspond to the traditional Belgian subdivision. From a hydrogeological point of view the KI-k-2 (Brunssum I) and KI-k-3 (Brunssum II) clay units are most relevant and can be recognised by their resistivity minima.